As far as messing with batteries? I am not aware of any issues.
Modifying the car for different batteries? I don’t think there is anything there either.
I think the real issue is modifying the cars outside the parameters set for NEV’s and taking them beyond their specific purpose and more/less outside their safety window. So far the safety police do not have their radar pointed in this direction.
In reality, the ability to go a bit faster makes the car safer from the standpoint of not backing up traffic behind them, but don’t forget about stopping. Early cars (which, being plentiful, most use as a their first base for hotrodding) have horrible brakes!!! The brake drums are the size of tuna cans and have suspensions copied from go cart tech.
An inertia benefit? - Switching to Lithium will automatically help with stopping distance because you are ditching several hundred pounds of lead.
But these are both topics best left for other threads and way off the original discussion.